In the art, magnetic bearing devices are well known in which a rotor is supported for rotation around a rotation axis by a set of active magnetic bearings. These active magnetic bearings are generally arranged within a housing together with a set of displacement sensors. The sensor signals are fed to a controller external to the housing, and depending on these signals, electric currents are provided to the magnetic bearings by the controller. Therefore, an electrical feedthrough for connections between the bearings and sensors within the housing and the controller outside of the housing through a wall of the housing is required. In many applications, such a feedthrough must be sealed in a gastight manner because of the presence of pressure differences between the inside and the outside of the housing. An important application is a turbo-molecular pump whose rotor carrying the rotor blades is supported by a magnetic bearing device. During operation of such a pump, the rotor and thus the inside of the housing will be at high-vacuum conditions, i.e., in the range below 0.1 mbar, while the outside is generally at ambient pressure. Therefore, any electrical feedthrough between the inside and the outside must be efficiently sealed to prevent vacuum losses.
Vacuum-tight electrical feedthroughs are well known in the art. In particular, so-called multipin feedthroughs are known which are placed into a small circular opening in a wall of the housing and which provide a plurality of connections in a single feedthrough. Due to the necessity of individually sealing a large number of wires, manufacture of such feedthroughs is relatively expensive, and the cost of the feedthrough may thus contribute significantly to the total cost of the magnetic bearing device. Additionally, multipin feedthroughs may be rather bulky, which hampers the development of small, low-cost magnetic bearings.
In WO-A 2005/038263 it has been suggested to reduce the number of wires which need to be fed through a wall of the housing by casting certain control circuits in a resin and disposing these circuits within the housing instead of outside of the housing. These circuits may, however, be exposed to a hostile environment (vacuum or aggressive gases and high temperatures) within the housing, which decreases the lifespan of the circuits, and the circuits are inaccessible from the outside for servicing, e.g., for an exchange in case of a hardware failure.